Probe storage devices have been developed to provide small size, high capacity, low cost data storage devices. Probe recording requires relative movement between a storage medium and an array of probe transducers that are used to subject the storage medium to electric, magnetic, or other fields. The storage medium can be a planar thin film structure.
Probe-based data storage devices use a large number of probe transducers that move over a storage medium surface, with each probe needing to move only a relatively small distance with respect to the medium, in a manner similar to a Scanning Probe Microscope (SPM). To maximize the achievable recording density, the probes are generally operated in physical contact or near-contact with the surface of the storage medium.
Scanning probe storage devices based on a ferroelectric storage medium include one or more transducers, each including an electrode or tip that moves relative to a ferroelectric thin film storage medium. To write a bit to the storage medium, a voltage pulse of either positive or negative polarity is applied between the electrode and the medium, and a binary “1” or “0” is stored by causing the polarization of a spatially small region (i.e., a domain) of the ferroelectric storage medium near the tip to point “up” or “down”. Data can then be read out by a variety of means, including sensing of piezoelectric surface displacement, measurement of local conductivity changes, or by sensing current flow during polarization reversal (i.e., destructive readout).
Destructive readout can be performed by applying a read voltage of a magnitude and polarity such as to cause the polarization to point “up”. Domains polarized “down” (e.g., representing “0”) will then switch to the “up” state, and a charge will flow which is proportional to the remanent polarization of the ferroelectric storage medium. Domains polarized “up” will have no such current flow. The presence or absence of this current flow, as determined by a sense amplifier, can then be used to determine whether the domain had contained a “1” or “0”.
Probe storage devices can provide a high data storage capacity in a very small form factor. In one example, a device having a capacity of 20 GB requires a density of 880 Gb/in2. The device of this example requires a track width of 50 nm, which places difficult requirements on the servo system accuracy. Current transducer designs use the same conductor for both reading and writing, which places a strong limit on Write-to-Read Track MisRegistration (WRTMR). Write-to-Read Track MisRegistration is the positioning requirement based on the need to read written signals with sufficient signal-to-noise ratio (SNR). Write-to-Write Track MisRegistration (WWTMR) is the positioning requirement based on the need to not overwrite adjacent tracks.
There is a need for a data storage device that can provide a large amount of data storage but have less restrictive track misregistration requirements.